An oscilloscope uses a two-axis graph to give a visual representation of a waveform over time, with the horizontal axis representing time and the vertical axis representing the amplitude. Oscilloscopes are frequently used to assist dynamics processing and sound synthesis. It's usually placed last in the signal chain, so that it analyses the cumulative effects of any plugins placed before it. Like any analysis plugin, though, you can place it anywhere in the chain, to view the signal at that point.